This invention relates to electrophotographic document copiers and/or printers and more particularly to automatic adjustment of parameters influencing reproduction by such copiers or printers.
In typical commercial electrophotographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged, charge-retentive, photoconductive recording member. Pigmented marking particles are attracted to the latent image charge pattern at a developing station to develop such image on the recording member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the recording member, and an electric field applied to transfer the marking particle developed image to the receiver member from the recording member. After transfer, the receiver member bearing the transferred image is transported away from the recording member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
The contrast density and color balance (in color machines) of electrophotographic reproduction apparatus frequently vary depending on a variety of factors. Some of these factors, such as the sensitometry of the recording member, are intrinsic to the recording apparatus. Other factors, such as the ambient humidity and the charge density of the marking particles, are extrinsic to the reproduction apparatus.
To compensate for these factors, the contrast density and color balance of a copier or printer can be adjusted by changing certain process control parameters such as primary voltage V0 and global exposure E0. Control of such parameters is often based on measurements of the density of a marking particle image in a test patch. Typically, the test patch can be recorded on an area of the electrostatic recording member between adjacent image frames and developed. The developed density of the patch can be measured and adjustments made accordingly.
Existing methods and apparatus for adjusting V0 and E0 are limited in that they attempt to adjust for all factors affecting contrast density and color balance collectively. Compensating for all factors collectively is complicated because the separate effects of the various factors are confounded, and therefore it is difficult to achieve extremely low margins of error. Accordingly, there is a need for a method and apparatus for adjusting V0 and E0 that isolate variations in contrast density and color balance that are caused by different factors so that corrections can be made for independent factors independently.
Many existing methods and apparatus are also limited in that they require an iterative process to adjust V0 and E0 to acceptable levels, thereby expending substantial amounts of time and marking particles during the adjustment process. Accordingly, there is a need for a method and apparatus for adjusting V0 and E0 in which the corrective changes are not iterative.
Current high-speed reproduction apparatus place a further limitation on process control methods for adjusting V0 and E0. The high-speed nature of typical reproduction apparatus requires on-board corrective calculations that can be performed quickly during reproduction. This precludes the real-time resolution of transcendental equations to adjust V0 and E0 because the necessary calculations require too much time. Accordingly, there is a need for a method and apparatus for adjusting V0 and E0 that includes linear equations for calculating corrective changes.
It is therefore an object of the present invention to provide a process control method and apparatus that isolates variations in the sensitometry of the recording member and compensates for these variations. It is also an object of this invention to provide a process control method and apparatus that compensates for variations in the sensitometry of the recording member without requiring iterative corrective changes to V0 and E0. It is yet another object of this invention to provide a process control method and apparatus in which any necessary real-time calculations for corrective changes to V0 and E0 are based on linear equations.
In accordance with the present invention, an improved electrophotographic recording process control method and apparatus are provided.
According to one aspect of the present invention, an electrophotographic reproduction apparatus is provided. The reproduction apparatus includes an electrostatic recording member for supporting an electrostatic image. A charging station is provided for establishing a primary charge on the recording member, the primary charge being defined by a parameter V0. An exposing station having an exposure parameter E0 modulates the primary charge to form an electrostatic image on the recording member. A measuring device measures an exposed surface potential of the recording member after modulation by the exposing means. A controller adjusts the parameters V0 and E0 by directing the charging station to establish a standard primary charge V0S on the recording member, directing the exposing station to modulate the primary charge to form a first electrostatic control patch using a first test exposure level E1 and a second electrostatic control patch using a second test exposure E2. The controller also directs the measuring device to measure a first test surface potential V1 of the first control patch and a second test surface potential V2 of the second control patch. The controller calculates a measured intrinsic sensitivity bm and an intrinsic toe dm associated with the recording member using V1 and V2. The controller also calculates a corrective charge parameter V0l using dm, and a corrective exposure parameter, E0i, using bm and dm. The controller adjusts V0 to equal V0i, and adjusts E0 to equal E0i.
According to another aspect of the present invention, a method of controlling an electrophotographic reproduction process is provided. The surface of an electrostatic recording member in an electrophotographic recording apparatus is charged to a standard primary charge V0s. The standard primary charge on the recording member is then modulated using a first test exposure E1 to form a first exposed test area, and using a second test exposure E2 to form a second exposed test area. A first test surface potential V1 is measured in the first exposed test area and a second test surface potential V2 is measured in the second exposed test area. A measured intrinsic sensitivity bm associated with the recording member is calculated using V1 and V2. A measured intrinsic toe dm associated with the recording member also is calculated using V1 and V2. A corrective charge parameter V0i is calculated using dm, and a corrective exposure parameter E0l is calculated using bm and dm. V0 is then adjusted to equal V0l, and E0 is adjusted to equal E0i.
According to yet another aspect of the present invention, a method is provided for determining a linear equation for approximating a measured intrinsic sensitivity, bm, of a photoconductor charged to a primary charge, V0, in an electrophotographic recording apparatus. A first exposure E1, and a second exposure, E2, are selected. A plurality of random sensitometric pairs, are then generated, wherein each of the random sensitometric pairs includes a random intrinsic sensitivity, brand, and a random intrinsic toe, drand. A plurality of surface potential pairs are then calculated using the plurality of random sensitometric pairs, wherein each of the surface potential pairs includes a first photoconductor surface potential, V1, calculated using the first exposure, E1, and a second photoconductor surface potential, V2, calculated using the second exposure, E2. A set of constants, bm0, bm1, and bm2, are then successively approximated by using the plurality of surface potential pairs in the linear equation bm=bm0+bm1*V1+bm2*V2, to calculate a plurality of measured intrinsic sensitivities, bm, and by and selecting bm0, bm1, and bm2 to minimize the variance between the plurality of measured intrinsic sensitivities, bm, and the plurality of random intrinsic sensitivities.
According to still another aspect of the present invention, a method is provided for determining a linear equation for approximating a measured intrinsic toe, dm, of a photoconductor charged to a primary charge, V0, in an electrophotographic recording apparatus. A first exposure E1, and a second exposure, E2, are selected. A plurality of random sensitometric pairs are then determined, wherein each of the random sensitometric pairs includes a random intrinsic sensitivity, brand, and a random intrinsic toe, drand. A plurality of surface potential pairs are then calculated using the plurality of random sensitometric pairs, wherein each of the surface potential pairs includes a first photoconductor surface potential, V1, calculated using the first exposure, E1, and a second photoconductor surface potential, V2, calculated using the second exposure, E2. A set of constants, dm0, dm1, and dm2, is then successively approximated by using the plurality of surface potential pairs in the linear equation dm=dm0+dm1*V1+dm2*V2, to calculate a plurality of measured intrinsic toes, dm, and selecting dm0, dm1, and dm2 to minimize the variance between the plurality of measured intrinsic toes, dm, and the plurality of random intrinsic toes.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.